In the field of photomechanical processes, there are demands for photographic materials excellent in reproducibility of originals, stable processing solutions, simplification of replenishment and so on in order to cope with diversity and complexity of printed matter.
In particular, a line original used in the photograph-taking process is made by putting together photocomposed letters, handwritten letters, illustrations, halftone photographs and so on, so it has a mixture of images differing in density and line width from one another. Under such a situation, development of cameras for such processes, photographic light-sensitive materials and image forming methods as to duplicate line originals with good reproducibility have been strongly desired. In the photomechanical process for catalogs and large-sized posters, on the other hand, magnification (spread) or reduction (choke) of halftone photographs is prevailingly carried out. Since lines are sparsely present in the photomechanical process using expanded dots, photographs of blurred dots are taken. In the case of the reduction, the number of lines per inch becomes greater than those of the originals, so halftone photographs of the smaller dot areas are taken. Accordingly, image forming methods which can ensure much wider latitude than conventional ones have been required for retaining the reproducibility of halftone gradation.
As for the light source of a process camera, a halogen lamp or a xenon lamp is used. For the purpose of imparting the photograph-taking sensitivity to these light sources, photographic light-sensitive materials are generally subjected to orthochromatic sensitization. However, it has turned out that orthochromatically sensitized photographic materials undergo more strongly an influence of chromatic aberration, so the images formed therein tend to suffer deterioration in quality. The deterioration of this kind is more conspicuous when a xenon lamp is used as light source.
As a system which can meet the demand for wide latitude, it has been known that a lithographic silver halide photographic material comprising silver chlorobromide (having a silver chloride content of at least 50%) is processed with a hydroquinone developer in which the effective concentration of sulfite ion is extremely lowered (generally 0.1 mol/l or less) to obtain a line or dot image with a sufficiently high contrast and high optical density to clearly distinguish the image area from the non-image area.
In this system, however, the developer used is quite liable to air oxidation because of the low sulfite ion concentration, so various efforts and ideas have been made to maintain the developer activity constant. In the present situation, some of them, though practically used, are very slow in processing speed to result in the lowering of working efficiency.
Therefore, there has been a requirement for image forming systems of the kind which are not liable to the instability of image formation in the above-described developing method (lithographic developing system) by using a processing solution which has high storage stability upon development and, what is more, can provide superhigh contrast photographic characteristics. As one of such systems, there has been proposed a system wherein a surface latent image type silver halide photographic material containing a specific acylhydrazine compound as an additive is processed with a developer which contains a sulfite preservative in a concentration of at least 0.15 mol/1 and is adjusted to pH 11.0-12.3 to produce a superhigh contrast negative image with a gamma value greater than 10, as disclosed in U.S. Pat. Nos. 4,166,742, 4,168,977, 4,221,857, 4,224,401, 4,243,739, 4,272,606 and 4,311,781. This new image-forming system has a characteristic that silver iodobromide and silver chloroiodobromide can be used in addition to silver chlorobromide, in contrast to the conventional system for forming a superhigh contrast image wherein only silver chlorobromide with a high chloride content is usable.
While the foregoing image forming system has excellent properties in respects of sharp quality of halftone image, stability and rapidity of processing, and reproducibility of an original, novel systems which can effect a further improvement in reproducibility of an original are desired in order to cope with the current diversity of printed matter. As for the lay out process and contact work, on the other hand, there is a striving for improvement in work efficiency through working in a better-lighted environment. With this aim, development of photographic materials for photomechanical use which can be handled in such an environment as to be called daylight in a substantial sense, and that of exposure printers have proceeded.
The term daylight photosensitive material as used herein describes a photographic material of the kind which can be handled safely for a long period of time using as a safe light the rays not including the ultraviolet portion but having in a substantial sense wavelengths of 400 nm or longer. The daylight photographic material to be employed in the lay out process and contact work is utilized for effecting negative-positive conversion or positive-positive reproduction by using as originals development-processed films having letter or halftone images, and subjecting the originals and a photographic material for contact work (hereinafter referred to as a "contact photographic material") to contact exposure, and it has been required of the daylight photographic material to have (1) the property of making it feasible for halftone, line and letter images to undergo negative image-positive image conversion faithfully in accordance with individual dot areas, line widths and letter image widths, respectively, and (2) the property of permitting the tone control of halftone images, and the line width control of line and letter images. So far, day light contact photographic materials capable of meeting such requirements have been provided.
However, in a high level of image-conversion work for forming letter images through the contact work from integrated originals, the conventional method of using a daylight photographic material and carrying out the contact work in daylight had a defect of providing letter images inferior in quality to those provided by the method of using a conventional darkroom contact photographic material and carrying out the contact work in a darkroom.
The method of forming letter images through the contact work from integrated originals is described in more detail below.
As shown in FIG. 1 hereinafter, a letter or line image-formed film (line original) (b) adhered to a transparent or translucent base (a) and a halftone image-formed film (half-tone original) (d) adhered to a transparent or translucent base (c) (wherein a polyethylene terephthalate film having a thickness of about 100 .mu.m is generally used as the adhesive base) are superposed, and employed as an original. The emulsion surface of a photographic material for contact work (e) is brought into direct contact with the halftone original (d), and subjected to optical exposure.
After the exposure, the photographic material is development-processed to produce blank areas corresponding to line images inside the halftone images.
A point of importance in such a method for forming letter images is that the ideal of negative image-positive image conversion consists in accomplishing the conversion faithfully in accordance with individual dot areas of a halftone original and individual line widths of a line original, respectively. However, as is apparent from FIG. 1, the exposure for printing the line original (b) on the contact photographic material is carried out in a condition that the base (c) and the halftone original (d) are sandwitched in therebetween, in contrast to the exposure carried out in a condition that the halftone original (d) is in direct contact with the emulsion surface of the contact photosensitive material.
Therefore, an exposure determined as optimum for accomplishing faithful negative image-positive image conversion with respect to the halftone original is out of focus for the line original because the base (c) and the halftone image (d) are interposed as a spacer. As the result, narrowing of the line width of the blank area corresponding to the line original is caused. This is responsible for deterioration in quality of the letter image.
With the intention of overcoming the above-described point at issue, systems using a hydrazine compound are disclosed in JP-A-62-80640 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-62-235938,JP-A-62-235939,JP-A-63-104046, JP-A-63-103235, JP-A-63-296031, JP-A-63-314541, and JP-A-64-13545. However, those systems cannot be said to be satisfactory, so it is to be desired that further improvements should be introduced thereinto.
As an attempt for making an improvement in image quality, there has been known a method of releasing a development inhibitor in such a distribution as to correspond to silver image from a redox compound containing a carbonyl group, as disclosed, e.g., in JP-A-61-213847. However, the method has defects that since the extension of halftone gradation is insufficient and the range of image-tone control is narrower than that in a lithographic development system; notwithstanding the use of the redox compound, the method cannot be a contrast development system to be submitted for photographing of halftone images; and further, as the nucleation activity becomes too high or insufficient depending on fluctuation in the developer composition (e.g., pH, sulfite ion concentration, etc.), the images obtained lack uniformity in quality to impair the value as commodities.
Therefore, development of photographic materials which enable the formation of high contrasty halftone images using a stable developer, and the control of image tone over a wide range has been desired.